If you have a good competitive moveset for Magmortar, post an answer below and upvote the best ones. Movesets for its pre-evolutions, if any, can also be shared on this thread.

Be sure to include full set details in your post, e.g. items, abilities, natures and EVs. Some detail, including the intended game mode for your set, is also appreciated. Access the full list of guidelines here.

Explanation

Despite its weakness to SR and early-game hazards, Magmortar is a great special Wallbreaker in NU with a very high Sp. Atk. It allows it to deal with bulky Pokemon, such as Audino, with ease.

Maximum investment in Sp. Atk is needed to deal enough damage. Investment in HP and Sp. Def allows it to take certain hits significantly easier. Usually, Assault Vest is preferred, but Expert Belt can be an option to deal more damage. Leftovers is an option, but it isn't as good as those two items. Vital Spirit is meant to counter many Sleep Powder users, such as Lilligant and Vileplume.

Fire Blast is preferred over Flamethrower for instant damage.
Thunderbolt is used for coverage against Water-types.
Focus Blast gives coverage against Rock-types that can wall this set (ex: Rhydon).
Finally, Psychic gives coverage against bulky Fighting-types, such as Gurdurr. Substitute can be used to take advantage of the various switches that Magmortar forces, but you would have to use Expert Belt.

Special sweeper right here. Flamethrower is obvious, while Thunderbolt covers water types. Focus Blast has some good coverage, but has 70 accuracy, HP Grass covers rock and ground, plus the water/ground types (I would choose HP Grass). Psychic has some good coverage, and can cover those fighting types that carry Earthquake /Rock Slide/Stone Edge.

Explanation: A simple Choise Scarf Special Sweeper. Psychic hits Nihilego along with a Chance to Lower the foe's Special Defense. Fire Blast is STAB with a burn chance. Thunderbolt hits Celesteela, Wishiwashi, and Toxapex for some good damage along with a paralysis chance. HP Grass covers all of Magmortar's weaknesses.

In my opinion this is the BEST Magmortar moveset .
Nature-Quiet . Item-Charcoal .

1-Hidden Power Grass
2-Flamethrower
3-Psychic
4-Overheat

MY REASONING- So, why no Solar Beam? Well, if an opponent switches into a Water or Ground Type, your'e already dead. Well Magmortar is. Solar beam takes 2 turns to charge and in 1, you will probably be destroyed by Hydro Pump or Surf. Sunny Day also takes away 1 move slot and1 turn to set. So that ins't very Super Effective. Hidden Power Grass might not be as powerful but is still a good coverage move. Flamethrower is a powerful STAB move and with Charcoal is incredible. Psychic is a decent coverage, replacement move for Flamethrower in case of a Gengar or PP runout. Finally Overheat is basically Explosion. Only use it when you are low on health. Running Charcoal and STAB on a base 120 move will give at least 160 damage BARE MINIMUM.

I hoped this answer helped your Magmortar needs. PS-On Showdown do a 252 on SP.ATK and SP.DEF as well as 4 on HEALTH.